In the manufacture of semiconductor devices and other ion related products, ion implantation systems are used to impart dopant elements into semiconductor wafers, display panels, or other types of workpieces. Typical ion implantation systems or ion implanters impact a workpiece with an ion beam utilizing a known recipe or process in order to produce n-type or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects selected ion species to produce the desired extrinsic material. Typically, dopant atoms or molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and implanted into a workpiece. The dopant ions physically bombard and enter the surface of the workpiece, and subsequently come to rest below the workpiece surface in the crystalline lattice structure thereof.
Several areas within an ion implantation system are negatively biased, for example, a suppression electrode, e.g., at approximately −1 KV, is often typical in the system. These systems also include an ion source extraction electrode, at the exit of an acceleration tube (or at an entrance of a deceleration tube), or generally, anywhere where a positive potential is used. Suppression electrodes will discourage or inhibit electron movement between two areas into which the suppression electrode separates. The suppression electrodes are usually mounted on small ceramic standoffs, since its negative potential is not very high and the weight of the electrodes is usually quite small (e.g., 100 grams or less).
The suppression electrode in the source extraction area is in a very hostile environment. First, the high energy, high flux ion beam causes sputtering of electrode and aperture materials (i.e., mostly metal and carbon) to coat unshielded insulative surfaces to make the surfaces conductive or in addition, build up conductive “flakes” which can and often eventually cause problems, for example, initiating high voltage sparks. Secondly, the vacuum environment is known to be a “dirty location”, often containing condensable vapor from within an ion source feed material and the vapor can “snake” through elaborate shielding structures to coat or deposit on the “hidden” insulative surface. Thirdly, related to the two reasons mentioned above, the suppression electrode has to endure frequent and high voltage sparks with large energy release (e.g., several Joules). Although typical ceramic standoffs are well protected by layer(s) of metal shields, those high voltage sparks often induce secondary sparks in the hidden insulative areas to cause sputter coating even in those hidden areas and worse case, insulators can crack because of a sudden surge current and rapid heating. Adding to all these deleterious environment factors, another fact is that the electrodes (e.g., suppression and ground electrodes) may have to be mechanically manipulated in position relative to the ion source, making the situation even more complicated.
Traditionally, a high voltage vacuum feed-through to supply a negative potential to the suppression electrode is located on a fixed flange of a manipulator assembly, although the suppression electrode itself moves with the manipulator. This arrangement not only requires a flexible wire or spring to connect the suppression feed through to the electrode, but also, the feed through itself is vulnerable to all the problems mentioned supra.
FIG. 1 illustrates a typical traditional arrangement of an extraction electrode manipulator 100 including an ion source 102 with source front plate 104 and an exit slit 106 formed in the front face of the ion source 102. The exit slit 106 allows an ion beam 108 to be extracted from the ion source 102. Insulating standoffs 110 are utilized to attach a suppression electrode 112 to a ground electrode 114 which allows the electrodes 112 and 114 to move in unison at a variable distance 118 from the ion source 102. The distance 118 is an important operational variable and has to be adjusted for the best properties of the exiting ion beam 108 according to ion beam energy, beam current density at the source slit 106 and mass of ions, all of which change from setup to setup. Also, side-to-side position 126 is adjustable to correct the angle of the exiting beam 108, which may come from misalignment of components or effect of the source magnetic field. These two motional adjustments are the function of extraction electrode manipulator 100. In this simplified mechanical extraction electrode manipulator 100 the metal bellows 120 is used to introduce the two motions, 118 and 126, in vacuum, but there are other methods of introducing motions in vacuum, like differentially pumped sliding seals.
As illustrated in FIG. 1 insulator shielding cups 116, surround the insulating standoffs 110, and a high voltage vacuum feedthrough 122 for suppression voltage of the simplified mechanical extraction electrode manipulator 100. Constant improvements have been tried on the shape and position of the insulating standoffs 110, involving different shapes, positioning and the number of layers of the shielding, but to date, the insulating standoffs 110 (i.e., suppression insulators) and suppression feedthrough 116 are still on (or near) the top list of periodical service list.
It is an object of the present invention, then to provide an improved extraction electrode manipulator by removing insulating standoffs and a high voltage vacuum feedthrough from the vicinity of ion beam, that require less maintenance and that result in fewer failures than previous manipulators.